Categories:: Aggregate Functions (General) , Window Functions (General, Window frame)

VARIANCE , VARIANCE_SAMP¶

Returns the sample variance of non-NULL records in a group. If all records inside a group are NULL, a NULL is returned.

Aliases:: VAR_SAMP

Syntax¶

Aggregate function

VARIANCE( [ DISTINCT ] <expr1> )

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Window function

VARIANCE( [ DISTINCT ] <expr1> ) OVER (
                                      [ PARTITION BY <expr2> ]
                                      [ ORDER BY <expr3> [ ASC | DESC ] [ <window_frame> ] ]
                                      )

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For details about window_frame syntax, see Window Frame Syntax and Usage.

Arguments¶

expr1: The expr1 should evaluate to one of the numeric data types.
expr2: This is the expression to partition by.
expr3: This is the expression to order by within each partition.

Returns¶

The data type of the returned value is NUMBER(<precision>, <scale>). The scale depends upon the values being processed.

Usage Notes¶

For single-record inputs, VAR_SAMP, VARIANCE, and VARIANCE_SAMP all return NULL. This is different from the Oracle behavior, where VAR_SAMP returns NULL for a single record and VARIANCE returns 0.
When passed a VARCHAR expression, this function implicitly casts the input to floating point values. If the cast cannot be performed, an error is returned.

When this function is called as a window function (i.e. with an OVER clause):
- If the OVER clause contains an ORDER BY subclause, then:
  - A window frame is required. If no window frame is specified explicitly, then the ORDER BY implies a cumulative window frame:
    
    RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
    
    For information about window frames, including syntax and examples, see Window Frame Syntax and Usage.
    
    For information about implied window frames, see also Window Frame Usage Notes.
  - Using the keyword DISTINCT inside the window function is prohibited and results in a compile-time error.

Examples¶

For examples, see VAR_SAMP.